| 2219aluminum alloy, a kind of high strength Al-Cu alloys, is an ideal materialfor the fabrication of the rocket fuel storage box. Aiming at solving the problems ofhigh porosities and low welding efficiencies in the conventional MIG weldingmethod of2219aluminum alloy welding process, plasma-MIG hybrid arc weldingis introduced, and the coupling mechanism of the hybrid arcs and the weldingprocedure are investigated. During the plasma-MIG hybrid arc welding process, thecoupling mechanism of outer plasma arc and inner MIG arc, hybrid arccharacteristics, spectral diagnostics information of hybrid arcs and the force modelof droplets are systematically studied by experimental and theoretical methods. Thetemperature distributions in the arc zones, the coupling mechanism of hybrid arcsand the effects of various welding parameters on the weld properties are disclosed,which enrich the theory of the plasma-MIG hybrid arc welding and provide theexperiment and theory basis for high quality welds of2219alloy with stableplasma-MIG hybrid arc welding procedure.The special welding torch is developed to meet the requirement of plasma-MIGhybrid arc welding, and the control system for the plasma-MIG hybrid arc weldingis also constructed to control the welding parameters by the use of PLC andhuman-machine engineering. Furthermore, a well designed arc starting system isrealized to solve the difficulty at arc starting during plasma-MIG hybrid arcwelding.The spectrum and image acquisition system for hybrid arcs, which is made upof the spectrometer, high-speed CCD digital cameras, narrow bandpass filters,Neutral filters and optical lens, can get the accurate full-field information of thearcs, and this system is simple in constructions with high accuracy and dataacquisition efficiency. Discrete Abel transfer algorithm is designed based onBockasten cubic polynomial interpolation method. The plasma-MIG hybrid arcfull-field information is available by converting the horizontal radiation strength toradial emitting coefficiency, and base on which the isothermal lines can be got inplasma-MIG hybrid welding process. The experimental results show that the highesttemperature zone in the arc center shifts due to the influence of inner MIG arc on outer plasma arc, and thus the highest temperature zone locate at the outer plasmaarc in plasma-MIG hybrid arc welding. There is a lowest temperature zone betweenthe outer plasma arc and the inner MIG arc, which locates at the interface of the twoarcs. The distributions of isothermal lines increase firstly, and then decrease, finallyincrease again, and they are centrosymmetrically distributed. The inner MIG arc iscompressed by the outer plasma arc for the constrict effect of the nozzle. The heateffect of MIG arc is weakened because of the bypass flow of the MIG current intothe plasma arc, and thus the temperature of MIG arc is lowered.With referencing to the mechanical theory of droplet transfer in conventionalMIG welding, the influence of outer plasma arc on the changing of droplet transferbehavior is further analyzed and a mechanical physical model is developed in thePlasma-MIG welding process. According to the theory of arc heating effect and thestatic force balance, the force actions on the droplets are calculated and the relationsbetween welding parameters and force are also revealed. The Plasma-MIG hybridarc characteristic, droplet transfer behavior, the influencing factors of arccharacteristic are studied systematically by adopting droplet photos andsynchronous acquisition of electrical parameters. Compared with conventional MIGwelding, the hybrid arc welding process is further stability, and thus non-spatterwelding process with difference of droplet transfer modes can be achieved.The quadratic regression mode with five factors is used to study the effects ofsingle factor and interactions multi-factor on tensile strength. The results show thatthe effect of single factor on tensile strength display parabola rules, welding speedis the greatest impact on the tensile strength, MIG voltage and Plasma current issubsequent effect, and the wire feed plays minimal role to tensile strength. The bestof interaction weld parameter is existed; the interactions between welding speed andwire feed are the greatest impact on the tensile strength, and meanwhile theinteractions between MIG voltage and welding speed which are mutuallyindependent play minimal role to tensile strength. The welding process parametersof2219aluminum are optimized by the mathematical treatment of the quadraticregression mode with five factors, the tensile strength of weld joint is285Mpawhich is the70.3%of base metal.The thermal cycling curve of Plasma-MIG welding for2219aluminum alloy isinvestigated. In the condition of five different kinds of parameters, the temperature gradient, residence time of high temperature and super cooling are analysised. Theinfluence of plasma arc on the motion of weld pool has been researched. It wasfound that the process of proton in arc atmosphere dissolving into liquid metal hasbeen controlled, the motion form of weld poor behavior is changed and theevolution of saturated gas has been accelerated due to introduction of outer plasmaarc. Compared with conventional MIG welding, the joint properties and weldmicrostructure of2219aluminum alloy are improved by Plasma-MIG hybrid arcwelding. |
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